My first version usually is 0.01. And the one after that is 0.02. I continue adding 0.01 for every subsequent release, unless a large portion was rewritten (bump to the next x.x0), or almost everything was rewritten (bump to the next x.00).
But if a module is at 0.xx even though it's in production use, profiled well, and has no known bugs *after a lot of use*, I might add 1 to the version, so that 0.24 can become 1.24. This is because users do indeed for some reason appear to think that the version number actually has meaning.
Well, unless you know how a certain author uses the digits available, IT DOESN'T MEAN A THING. Proof: File::Slurp.
The only rules are that a newer version must have a higher version number, and that the CPAN indexers understand your format.